Police advice to the Tate Modern Art Gallery, that one of the pictures in their current "Pop Life" exhibition may be child porn, and therefore illegal to display, highlights yet again the difficulty of policing this sort of material in an internet age.

The picture in question is Spiritual America, by reputable photographer Richard Prince, and is a study of actress Brooke Shields – at age 10. She is naked, heavily made-up and provocatively posed. Although this picture has been exhibited on a number of occasions in the United States, this is the first time it has been brought to the UK.

On any reading of the existing law on indecent images of children – the Protection of Children Act 1978 – there is a strong likelihood that this would count as an indecent image.

Readers tempted to bring up the image in Google should bear this in mind: under UK law, if a picture is indecent, then possession of that image is an offence. With a few specific exemptions – most notably around research, forensics and law enforcement – there is no opt-out from that harsh fact of legal life: idle curiosity would certainly not count as an excuse in court.

According to the Metropolitan Police, who have met with Tate management to discuss this matter: "[we] are keen to work with gallery management to ensure that they do not inadvertently break the law or cause any offence to their visitors".

The Tate have now taken the picture down temproarily and are in discussion with the police.

However, the mere fact that this matter has been widely reported is likely to drive individuals to go looking for it online and - it would not be too far-fetched to predict – some individuals may reach the same conclusion as this author: that the picture is almost certainly illegal under existing law. The Crown Prosecution Service sets out five levels of seriousness in respect of indecency, with level one being characterised by no more than "sexual posing". This picture appears to fall into that category.

Therefore, a complaint to the Internet Watch Foundation (IWF) may yet be inevitable: in which case, they will have to decide whether to add sites carrying this image to their block list and risk a backlash of the sort that occurred last year, when they attempted to block an image – an album cover for German rock group The Scorpions – or take a more pragmatic approach, and allow it to continue to circulate.

That, in turn, would open up a curious double standard between the ability of the authorities to police real life and online.

No such complaint has yet been made, and the IWF would not be drawn into commenting on something that is "purely hypothetical": a sensible move, as this could yet turn into another no-win situation for them. This conflict of means and objectives does, nonetheless, serve to highlight a continuing tension in the law, that is likely to prevail as long as individuals are subject to prosecution for possession of certain images, irrespective of intent. ®